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Studies of Calcium and Phosphorus Metabolism in the Chick

III. Some Time Relationships in the Action of Vitamin D¹

Research Laboratories. Winthrop Chemical Company, Inc., Rensselaer, New York

The baby chicks used in this study had a supply of vitamin D adequate for about 14 days of life. Their calcium and phosphorus retentions then reached a level of about 20 mg. per 100-gm. chick per day, a level which they were able to maintain for 3 weeks. After this there was a decline to very low levels as the birds went into a state of terminal rickets. However, chicks which received oral supplements of vitamin D₂ or D₃ showed an immediate increase in calcium and phosphorus retentions. The improvement was evident for 7 or 8 days, after which the chicks returned to the same low level of retention. A second vitamin supplementation of the same magnitude produced a positive, but quantitatively inferior, effect, probably due to the intervening growth of the birds. Following supplementation, the increased level of mineral retention was directly related to the amount of vitamin D available. The body content of vitamin D₂ following an oral dose of 2400 I.U. increased to about 1000 I.U., and, in the ensuing 10 days, fell to about 250 I.U. This residue, equivalent to about 6 I.U. of vitamin D₃, appeared to be rather tenaciously conserved.

Manuscript received 13 October 1944.